Abstract

The ultrafast dynamics of clusters of trans-azobenzene anion solvated by oxygen molecules was investigated using femtosecond time-resolved photoelectron spectroscopy. The time scale for stripping off all oxygen molecules from was determined by monitoring in real time the transient of the rise, following an excitation of , where . A careful analysis of the time-dependent photoelectron spectra strongly suggests that for a quasi- core is formed and that the dissociation occurs by a bond cleavage between and conglomerated rather than a stepwise evaporation of . With time and energy resolutions, we were able to capture the photoelectron signatures of transient species which instantaneously rise then decay. The transient species are assigned as charge-transfer complexes: for and for , where . Subsequent to an ultrafast electron recombination, rises with two distinct time scales: a subpicosecond component reflecting a direct bond rupture of the nuclear coordinate and a slower component (, increasing with ) attributed to an indirect channel exhibiting a quasistatistical behavior. The photodetachment transients exhibit a change in the transition dipole direction as a function of time delay. Rotational dephasing occurs on a time scale of , with a change in the sign of the transient anisotropy between and the larger clusters. This behavior is a key indicator of an evolving cluster structure and is successfully modeled by calculations based on the structures and inertial motion of the parent clusters.